1. Field of the Invention
This invention relates to laser-guided projectiles and more particularly to an optically-coupled communication interface using SAL seeker.
2. Description of the Related Art
Laser guided ordinance is commonly used to engage point targets with a high probability of success and minimal collateral damage. Such ordinance includes guided artillery projectiles, guided missiles, and guided bombs, all of which will be referred to herein as “laser-guided projectiles”.
A laser-guided projectile includes a semi-active laser (SAL) seeker to detect pulsed IR laser electro-magnetic radiation (EMR) scattered from the intended target and to provide signals indicative of the target bearing such that the projectile can be guided to the target. The SAL includes a non-imaging optical system to capture and focus the scattered laser EMR onto a detector assembly. The optical system convert the target bearing to an irradiance distribution or “spot” positioned on the detector. As the target bearing changes the position of the spot on the detector changes.
Referring now to FIG. 1a, soldier A 10 inputs pre-launch data required by the projectile 12. Pre-launch data may include the guidance mode, fuze timing mode, fuze detonation mode, range to target, target location, lock mode or atmospheric conditions. The pre-launch data may be input via a hardwired interface between the launch tube and the projectile, an RF interface, an electro-magnetic inductive interface or a mechanical interface such as a rotary clicking switch. The specific interface is dictated by the weapon system. Soldier A places projectile 10 into a launch tube 14 (or rack or some other launch platform).
Referring now to FIG. 1b, soldier B 16 uses a laser designator 18 to illuminate a target 20 with pulsed laser radiation 22. The target is represented as a tank, but may be another type of vehicle, ship, boat, or a structure, building or other stationary object. Laser designators radiate in a narrow beam of pulsed energy. Current tactical lasers operate in the near IR wavelength spectrum, which is not visible to the human eye. They can be aimed so the energy precisely designates a chosen spot on the target. The laser designator may be located on the ground, as shown in FIG. 1b, or may be located in a vehicle, ship, boat, or aircraft. An automated tracking system may be used to point the designator to illuminate the target.
Soldier A points the launch tube at the target to acquire the scatter laser radiation 24 from the target 20 and fires the projectile. Laser guided projectile 12 engage target 20 by detecting and following scattered laser radiation 24 from the target 20. The laser guided projectile 12 includes a projectile body, a warhead, control surfaces, and a guidance system. The guidance system includes a SAL seeker and a flight computer to control the flight of the laser guided projectile by manipulating one or more control surfaces based on at least one guidance signal from the SAL seeker. The control surfaces may be canards fins, wings, ailerons, elevators, spoilers, flaps, air brakes or other controllable devices capable of affecting the flight path of the laser guided projectile.
Laser designators and seekers use a pulse coding system to ensure that a specific seeker and designator combination work in harmony. Pulse coding is typically based on Pulse Repetition Frequency (PRF) coding. By setting the same code 26 in both the designator and the seeker, the seeker will track only the target designated by the designator. Current pulse codes use a truncated decimal system that uses the numerical digits 1 through 8, and the codes are directly correlated to a specific PRF. Typical equipment uses either a three or four-digit code. The designator repeats the code in the emitted pulsed laser beam that is directed at the target to “paint” the target and reflected back to the seeker. The seeker may be configured to recognize multiple different codes. The seeker verifies the code embedded in the pulsed laser radiation. Details of PRF coding for laser-designated weapons are provided in U.S. Pat. Nos. 5,023,888 and 5,026,156, which are hereby incorporated by reference.